Conformal low temperature hermetic dielectric diffusion barriers

ABSTRACT

Conformal hermetic dielectric films suitable as dielectric diffusion barriers over 3D topography. In embodiments, the dielectric diffusion barrier includes a dielectric layer, such as a metal oxide, which can be deposited by atomic layer deposition (ALD) techniques with a conformality and density greater than can be achieved in a conventional silicon dioxide-based film deposited by a PECVD process for a thinner contiguous hermetic diffusion barrier. In further embodiments, the diffusion barrier is a multi-layered film including a high-k dielectric layer and a low-k or intermediate-k dielectric layer (e.g., a bi-layer) to reduce the dielectric constant of the diffusion barrier. In other embodiments a silicate of a high-k dielectric layer (e.g., a metal silicate) is formed to lower the k-value of the diffusion barrier by adjusting the silicon content of the silicate while maintaining high film conformality and density.

CLAIM OF PRIORITY

The present application is a divisional of co-pending U.S. patentapplication Ser. No. 13/976,835, filed Jun. 27, 2013, which is a U.S.National Phase application under 35 U.S.C. §371 of InternationalApplication No. PCT/US2011/066252, filed Dec. 20, 2011, entitled“Conformal Low Temperature Hermetic Dielectric Diffusion Barriers”.

TECHNICAL FIELD

Embodiments of the present invention generally relate to semiconductordevices, and more particularly to conformal dielectric diffusionbarriers.

BACKGROUND

Microelectronic devices, such as integrated circuits incorporatingmetal-oxide-semiconductor transistors (MOSFETs), or the like, continueto scale by reducing pitches between adjacent features and incorporatingthree-dimensional transistor structures (e.g., finFETs). As transistordensity and non-planarity increases, so too does the interconnectmetallization, increasing interconnect capacitance and making electricalisolation more difficult. Interconnect processes over the last decadehave increasingly incorporated “low-k” films (e.g., those below ˜3.2) asthe material of choice of inter-level dielectrics (ILDs), some furtherimplementing air gap formation whereby voids in the ILD between adjacentmetal lines are deliberately introduced. Also, topography present due toradical 3D structures may induce voids and/or defects that need to besealed/covered by a conformal dielectric layer.

Plasma enhanced chemical vapor deposition (PECVD) processes aretypically used for dielectric deposition in low-k interconnectapplications but do not offer high conformality/step coverage. Forexample, a PECVD low-k film typically has conformality less than 55%(e.g., only approaching 75% with a dep/etch/dep type sequence) where adielectric has deposited thickness on vertical (e.g., sidewall) surfacethat is less than 55% of the deposited thickness on a horizontal (e.g.,top) surface. CVD or low pressure CVD (LPCVD) techniques offer higherconformality, but require temperatures higher than typically permissiblefor low-k interconnect applications.

It is often desirable to provide a hermetic seal with a dielectriclayer, for example to prevent out-diffusion of metal (e.g., Cu) from ametal interconnect line into surrounding ILD material, as well as toprevent moisture and wet chemical in-diffusion from surrounding ILD (orfrom a void in an air gap formation process) into a 3D structure (e.g.,metal line, transistor, etc.). Due to difficulties in achieving perfectcoverage and film densification over 3D topography, there is therefore aminimum thickness requirement for a dielectric diffusion barrier.

Materials and techniques to reduce a dielectric diffusion barrierminimum thickness are therefore advantageous.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are illustrated by way of example,and not by way of limitation, and can be more fully understood withreference to the following detailed description when considered inconnection with the figures in which:

FIG. 1 is a flow diagram illustrating a method of forming a dielectricdiffusion barrier, in accordance with an embodiment;

FIGS. 2A, 2B, 2C, 2D, 2E, 2F, 2G, and 2H illustrate side views of across section through an IC fabricated in accordance with an embodimentof the method illustrated in FIG. 1;

FIGS. 3A-3B illustrate line graphs for experimental evaluations ofdielectric diffusion barrier embodiments, in accordance with embodimentsof the present invention; and

FIG. 4 is a functional block diagram of a mobile computing platformwhich may incorporate ICs fabricated in accordance with the methodillustrated by FIGS. 1 and 2A-2G.

DETAILED DESCRIPTION

In the following description, numerous details are set forth, however,it will be apparent to one skilled in the art, that the presentinvention may be practiced without these specific details. In someinstances, well-known methods and devices are shown in block diagramform, rather than in detail, to avoid obscuring the present invention.Reference throughout this specification to “an embodiment” means that aparticular feature, structure, function, or characteristic described inconnection with the embodiment is included in at least one embodiment ofthe invention. Thus, the appearances of the phrase “in an embodiment” invarious places throughout this specification are not necessarilyreferring to the same embodiment of the invention. Furthermore, theparticular features, structures, functions, or characteristics may becombined in any suitable manner in one or more embodiments. For example,a first embodiment may be combined with a second embodiment anywhere thetwo embodiments are not mutually exclusive.

The terms “coupled” and “connected,” along with their derivatives, maybe used herein to describe structural relationships between components.It should be understood that these terms are not intended as synonymsfor each other. Rather, in particular embodiments, “connected” may beused to indicate that two or more elements are in direct physical orelectrical contact with each other. “Coupled” my be used to indicatedthat two or more elements are in either direct or indirect (with otherintervening elements between them) physical or electrical contact witheach other, and/or that the two or more elements co-operate or interactwith each other (e.g., as in a cause an effect relationship).

The terms “over,” “under,” “between,” and “on” as used herein refer to arelative position of one material layer with respect to other layers. Assuch, for example, one layer disposed over or under another layer may bedirectly in contact with the other layer or may have one or moreintervening layers. Moreover, one layer disposed between two layers maybe directly in contact with the two layers or may have one or moreintervening layers. In contrast, a first layer “on” a second layer is indirect contact with that second layer.

Described herein are conformal hermetic dielectric films suitable fordielectric diffusion barriers over 3D topography. In embodiments, thedielectric diffusion barrier is a dielectric layer which is deposited byatomic layer deposition (ALD) techniques to achieve a conformality of atleast 95% for a thinner contiguous diffusion barrier than can beachieved in a conventional silicon dioxide/nitride/carbide-based film,for example deposited by PECVD or by a repetitive deposition/sputterplasma enhanced chemical vapor deposition (PECVD) process capable of aconformality of no more than 75%. Because the ALD dielectric layer mayhave a relatively higher dielectric constant than such PECVD films, itmay be counter intuitive to employ such a material in structuressensitive to capacitance, however it has been found the excellent stepcoverage and greater mass/atomic density of certain “high-k” dielectriclayer materials enables a hermetic diffusion barrier of reducedthickness. Generally, this high mass and/or high atomic density impliesno (or very low) porosity with interstitial spaces in the barriermaterial being of such a small dimension that it is difficult fordiffusing atoms to pass through the barrier material (i.e., a moretortuous diffusion path).

Thus, for a diffusion barrier, the tradeoff between a moderate k filmwith only moderately good step coverage and hermeticity and a higher kfilm with better step coverage and hermeticity can be made favorable.For example, in certain applications, this reduction in thickness of thediffusion barrier enables a net reduction in capacitance of a structure(e.g., an interconnect ILD level) by increasing an available volume foran extremely low dielectric (e.g., a volume for an air gap).

In further embodiments, the dielectric constant of the diffusion barrieris advantageously reduced by where the barrier is made a multi-layeredfilm including the relatively high-k ALD layer and a low-k orintermediate-k dielectric layer (e.g., a bi-layer). In other embodimentsa silicate of the relatively high-k ALD layer is formed to takeadvantage of the conformality and density of the ALD dielectric, butlower the k-value of the diffusion barrier by adjusting the siliconcontent of the silicate.

FIG. 1 is a flow diagram illustrating a method 100 for forming adielectric diffusion barrier, in accordance with an embodiment whereinterconnect metallization in ILD incorporates air gaps between adjacentmetal structures of a same metallization layer (e.g., metal lines). Adielectric diffusion barrier is disposed between the air gap sidewallsof the metal lines to protect the interconnect metallization. While theexemplary interconnect embodiments serves as useful illustrations, it isnoted that the dielectric diffusion barrier materials and depositiontechniques described in the exemplary interconnect context areapplicable in many other contexts where a dense, conformal hermeticdielectric diffusion barrier is needed over severe 3D topography. Forexample, one of skill in the art may readily implement the teachingsprovided herein to form a diffusion barrier disposed over a finfet, aliner of a shallow trench isolation region, a passivation layer of awaveguide in a photonic integrated circuit, etc. The teachings providedherein are also applicable for some 2D applications such as forming verythin, hermetic Cu capping layers in dual damascene structures.

Method 100 begins at operation 110 with the formation of a low-k ILDstructure. FIG. 2A illustrates a side view of a cross section through anintegrated circuit (IC), such as a microprocessor or other logic device,fabricated in accordance with an embodiment of the method 100. In FIG.2A, transistors of the IC are disposed in the substrate 201. Thesubstrate 201 may include any conventional semiconductor substrate(e.g., silicon, Ge, SiGe, SiC, GaAs, InP, GaN, etc.), whether in a bulkor SOI format, as wells as polymer substrates (e.g. in TFTapplications). Transistors disposed in the substrate 201 may be of anyconventional design, such as, but not limited to, planar or non-planarMOSFETs, planar or non-planar high electron mobility transistors(HEMTs), etc.

Disposed over the substrate 201 is a low-k ILD structure comprising alow-k dielectric layer 210 in which a first metal interconnect level 205is embedded, for example by any dual damascence process known in theart. In the exemplary embodiment, the low-k dielectric layer 210 is acarbon-doped oxide (SiOC:H) having a dielectric constant in the range of2.5-3.2, depending on porosity. Of course, other known low-k ILDmaterials may also be utilized, and indeed in the exemplary embodimentwhere the low-k dielectric layer 210 is in some respects is sacrificial(as discussed elsewhere herein), it is also possible to uses in place ofthe low-k dielectric layer 210 a layer of a convention moderate-kdielectric material, such as SiO₂, PSG, BPSG, SiOF, etc. In embodiments,each metal interconnect line 205 comprises a barrier layer, such astantalum (Ta) or TiN, and a fill metal, such as copper (Cu) or tungsten(W).

Continuing with the method 100, at operation 130 trenches are etchedinto the low-k ILD around the metal interconnects. Generally, operation130 entails rendering a planar damascene layer non-planar for the sakeof introducing voids into spaces between the metal interconnect lines.It is this introduction of extreme topography which provides anexemplary impetus for the highly conformal dielectric diffusion barriersdescribed herein. As one example of forming such trenches, FIG. 2Billustrates a side view of a cross section through the integratedcircuit (IC) illustrated in FIG. 2A following deposition of a hard masklayer 220A over the low-k ILD structure. The hard mask layer 220A may beany material known in the art to be suitable for such purposes, such as,but not limited to, a low-k SiN:H, SiC:H, SiOC:H, SiCN:H, or SiOCN:H (asthe hard mask layer 220A is typically deposited by PECVD, a significantamount of hydrogen is incorporated into the films). The thickness of thehard mask layer 220A may range from about 2-50 nm and dielectricconstant (k) of the material may range from 4-7. In the exemplaryembodiment, thickness is about 8 nm and k is about 4.8. Notably, inaddition to aiding patterning, the hardmask layer 220A also serves toprotect the top surface of the metal interconnects from oxidation andcorrosion during fabrication. In exemplary embodiment, the hardmasklayer 220A is non-sacrificial, remaining in place to passivate the (Cu)surface of the metal interconnects and should therefore have goodadhesion to minimize mechanical and electromigration failures.

Continuing with the exemplary implementation of operation 130, FIG. 2Cillustrates a deposition of additional masking layers to form amulti-layered mask and patterning of the multi-layered mask. Disposedover the hard mask layer 220A is a second hard mask layer 220B, such as,but not limited to, amorphous carbon (α-C:H), TiN, or TaN. Over thesecond hard mask layer 220B is any conventional photoresist 220C, and anorganic anti-reflective coating (ARC), and/or dielectric ARC (DARC)220D, such as, but not limited to a silicon-containing material likesilicon dioxide, silicon nitride, carbon doped oxide, etc. Thepatterning is such that openings 225 are formed over the low-kdielectric layer 210 in the spaces between two adjacent metalinterconnect lines (e.g., 205A and 205B).

FIG. 2D completes the exemplary implementation of operation 130 withetching of the trenches 230 in the low-k dielectric 210 disposed betweenadjacent metal interconnect lines 205A, 205B. Any plasma-based etches,such as but not limited to fluorinated chemistries (CF₄, C₂F₆, CF₃H,etc.) may be utilized to etch trenches 230 to extend at least partiallythrough the (partially sacrificial) low-k ILD layer 210 from a topsurface of the low-k dielectric layer 210, and may extend completelythrough the low-k dielectric layer 210 to expose the substrate 201. Itis, of course, understood that the trench 230 can also be formed by anyother known technique such as, but not limited to, ion milling and laserablation. The photoresist 220C, second hardmask layer 220B (e.g., TiN),and the other patterning materials are then removed using anycombination of dry plasma etching and wet chemical cleans known in theart (typically by an oxygen plasma or hydrogen plasma followed by a wetclean). Following the completion of operation 130, and as illustrated inFIG. 2D, the low-k ILD structure now includes extreme 3D topography withmetal interconnect lines (e.g., Cu) extending upward around trenches(vias) inlaid into the metal interconnect lines 205 where portions ofthe low-k dielectric layer 210 have been removed. In embodiments, thetrench 230 has an aspect ratio of at least 5:1 and greater than 7:1 inthe exemplary embodiment. Notably, although the hardmask layer 220A isretained as a non-sacrificial layer in the exemplary embodiment, thehard mask layer 220A may not remain intact due to corner rounding duringthe etching of the trench 230 or may be completely removed by subsequentprocessing.

Returning to FIG. 1, the method 100 continues with conformallydepositing a hermetic dielectric diffusion barrier. In the exemplaryinterconnect embodiment, illustrated in FIG. 2E shows the dielectricdiffusion barrier 240 forms a contiguous liner in the trench 230,spanning the space between adjacent metal interconnect lines 205A, 205B,as well as covering the hardmask layer 220A.

In an embodiment, at least a portion of the hermetic dielectricdiffusion barrier 240 is deposited with an ALD process. Though ALD isgenerally known in the art, it is limited in application by thepractical constraints imposed by the availability of acceptableprecursors capable of self-limiting reactions to form a film of thedesired composition. Thus, while the widespread availability of certainpre-cursors has enabled ALD to become a popular technique for theformation of gate dielectric layers, such has not been true fordielectric materials employed in typical interconnect isolationcapacities. For this reason, plasma enhanced ALD (PEALD), a quasi-ALDtechnique, has been investigated as a means to deposit a wider varietyof materials, but films produced by this technique have been found to beuniformly hermetic only at thickness greater than about 16 nm andtherefore the quasi-ALD technique is not particularly advantageous fordielectric diffusion barriers. Hermetic barriers at thicknesses lessthan 5 nm are only possible with PECVD/PEALD technique where the film isdeposited on perfectly flat surfaces because of densification of thefilm from through ion bombardment during the deposition or sputtertreatments. However, because this ion bombardment is highly direction,film deposited on ion shadowed surfaces (e.g., near vertical surfaces)are of lower density and not hermetic. In the exemplary embodimentsdescribed herein, a true ALD process is employed to form a dielectricdiffusion barrier that is hermetic at thicknesses below 10 nm, moreparticularly below 8 nm, and most particularly below 6 nm. With the highconformality of the ALD process (e.g., 95% or more), it is possible toestablish a contiguous, pin-hole free film over extreme 3D topography atthese very low film thicknesses.

In an embodiment, prior to depositing the dielectric diffusion barrier240, a dielectric material is deposited by PECVD to avoid directexposure of any exposed surface of the metal interconnect lines (e.g.,Cu) which might be adversely affected by direct exposure to an ALDprecursor. If the hardmask 220A is fully in place and some amount oflow-k ILD is preserved on the interconnect line sidewall, the topsurface and liner of the interconnect line may be protected. However dueto imperfections, some low-k ILD may not remain on the sidewall and thetop interconnect surface may be exposed to corner clipping, partialetching or complete removal of the hardmask 220. Also, low-k ILDs arepour barriers and oxidation of the interconnect liner (Ta/TaN) remains apossiblity regardless. Exemplary dielectric materials suitable for thispurpose, include, but are not limited to, SiN:H, SiCN:H, SiC:H, SiOC:H(e.g., having a range of dielectric constants described elsewhere hereinfor the hardmask layer 220A) and may be deposited by PECVD to athickness preferably less than 2 nm, though alternate embodimentsinclude depositing the low-k interconnect passivation film to greaterthicknesses (e.g., 4 nm-16 nm).

In an embodiment, at least a portion of the hermetic dielectricdiffusion barrier 240 is an ALD dielectric material that has arelatively high dielectric constant compared to silicon-based PECVDfilms (e.g., greater than 6). There are many such films known in the artto be formable with the ALD technique and generally any of them may beemployed as the dielectric diffusion barrier 240, or a portion thereof.In the exemplary embodiment, the high-k dielectric material is a metaloxide such as, but not limited to, Al₂O₃, MgO₂, and HfO₂, all of whichhave a dielectric constant well over 10. Other transition metal oxides,such as TiO₂, TaO₂, and ZrO₂, that are also compatible with the ALDtechnique may be utilized in alternate embodiments.

Employing a true ALD technique, self-limiting reactions are successivelyperformed during the operation 140. For example, a 6-10 nm Al₂O₃ filmmay be deposited as the dielectric diffusion barrier 240 by sequentiallypulsing trimethylaluminum (TMA) and H₂O vapor, each precursorparticipating in a self-limiting reaction to iteratively form a veryconformal film. These sequential self-limiting reactions impart theadvantageous high conformality to the dielectric diffusion barrier 240at temperatures below those required to conformally deposit dielectricsin LPCVD processes. Also advantageous, the aluminum atom is large andtightly bonds with neighboring oxygen atoms to form a dense film capableof hermeticity at thicknesses below 8 nm and even below 6 nm (e.g., 3-4nm). While the exemplary embodiment of Al₂O₃ has been experimentallyverified, similar performance is expected of MgO₂ and HfO₂, and may alsobe expected of other high-k films known in the art to have similaratomic density. Thus, in the exemplary embodiment, ALD is utilized toachieve a contiguous dielectric film over extreme 3D topography even atthicknesses in the 5-10 nm range and the species employed in the ALDtechnique are ones which form a dense film capable of providinghermeticity at the minimum thickness required to form a physicallycontiguous film over the topography present.

While embodiments employing an ALD dielectric layer may of courseinclude more than one type of dielectric material (e.g., a bi-layer ofdistinct high-k materials), in an exemplary embodiment, an ALDdielectric layer is coupled with a distinct dielectric material layerhaving a dielectric constant below that of the ALD material. In one suchembodiment, the dielectric diffusion barrier 240 includes at least onemetal oxide layer 242, such as Al₂O₃, MgO₂, and HfO₂, and a moderate-kmaterial layer 243 having a dielectric constant below that of the metaloxide but above that of the surrounding low-k dielectric layer (e.g.,low-k ILD 210), as shown in FIG. 2H. In an exemplary embodiment, themoderate-k material is SiON(C):H. In such an embodiment the SiON(C):Hlayer is formed by first depositing by PECVD a SiO(C):H film and thensputter etching that SiO(C):H film with an plasma including a nitrogensource (e.g., one or more of NH₃, N₂) which sputters away part of thenon-conformally deposited material and redistributes it onto topographicsidewalls (e.g,. sidewalls of the trench 230). While the sputter etchdensifies the SiOC:H film and incorporates nitrogen to form SiON(C):H,such a film on its own would not be hermetic on ion-shadowed surfacesunless over 15 nm (e.g., 16 nm and above). However, with hermeticityenhanced by the ALD film and the dielectric constant of this moderate -kmaterial being in the range of 4.4-5.5 the dielectric diffusion barrier240 may have a reduced total capacitance.

In embodiments, the SiON(C):H and ALD dielectric form a bi-layer witheither the SiON(C):H forming a first layer or the ALD dielectric formingthe first layer. In the exemplary embodiment the bi-layer dielectricdiffusion barrier 240 includes a first layer of SiON(C):H and the ALDdielectric as a second layer disposed on the first layer. Exemplarythicknesses of the bi-layer dielectric diffusion barrier 240 are between5 and 10 nm with the SiON(C):H being between 3 and 6nm (e.g., slightlymore than half the total thickness of the dielectric diffusion barrier240). In one embodiment where a dielectric layer (e.g., SiOC:H) is firstdeposited to passivate a metal interconnect line prior to forming theALD dielectric layer, deposition of the passivating dielectric layer maybe transitioned into the first layer of the dielectric diffusion barrier240 by initiating the nitrogen-based sputter etch process to convert aportion of the passivating dielectric layer into the denser, moreconformal SiON(C):H film.

In further embodiments, the dielectric diffusion barrier 240 is atri-layer film stack 241 in which the ALD dielectric material (notshown) is disposed between PECVD deposited films (e.g., a base layer ofSiON(C):H (not shown) as in the case of a bi-layer embodiment and a caplayer of a SiON(C):H) which may improve adhesion and etch profiles inoverlying layer deposited in subsequent operations.

In another embodiment, the dielectric diffusion barrier 240 includes asilicon alloy of a metal oxide. The silicon alloy of the metal oxide inthe exemplary embodiment is formed by ALD (as opposed to an alloy formedby solid state diffusion of a discretely deposited film stack). In onesuch embodiment, at least one metal oxide is deposited in conjunctionwith silicon to form a conformal metal silicate film. In suchembodiments, the amount of silicon incorporated into the dielectricdiffusion barrier 240 may range from 1-90% (atomic) as selected toachieve a desired reduction in the dielectric constant of dielectricdiffusion barrier 240. For example, in one embodiment where the metaloxide is Al₂O₃, silicon is introduced to generate a Al_(1−y)Si_(y)O_(x)dielectric film. In one exemplary Al_(1−y)Si_(y)O_(x) embodiment, thesilicon content is at least 50% (atomic) to reduce the dielectricconstant of the alloy to below 7 while still providing a hermetic sealat thicknesses below 15 nm, and preferably below 10 nm. For example,during operation 140 an ALD sequence of TMA/H₂O/SiH₄/H₂O may beperformed with the duty cycle between TMA and SiH₄ varied to achieve thedesired silicon content. In alternative embodiments, other metalsilicates can be produced by analogous ALD processes incorporating otherexemplary metal oxides (e.g., MgO₂, HfO₂, etc.). In alternativeembodiments another alloying species other than silicon is employed tolower the dielectric constant of the dielectric diffusion barrier 240.For example, any of B₂O₃, BeO₂, L_(i2)O, Na₂O might be utilized.

As with a metal oxide layer, the alloyed dielectric utilized in thedielectric diffusion barrier 240 may include a base PECVD layer and/or acap PECVD layer in addition to the ALD metal silicate layer. Forexample, a metal silicate layer (Al_(1−y)Si_(y)O_(x)) may be disposed ona SiN:H, SiC:H, SiOC:H, or SiCN:H film or capped with a SiN:H, SiC:H,SiOC:H, or SiCN:H film. As another example, the metal silicate layer(Al_(1−y)Si_(y)O_(x)) is disposed between a cap and a base layer of anyof SiN:H, SiC:H, SiOC:H, or SiCN:H.

Returning to FIG. 1, method 100 continues at operation 150 with anon-conformal deposition of a low-k or moderate-k (e.g., SiO₂, PSG,BPSG, SiOF, polymer, etc.) ILD. In the exemplary interconnectembodiment, it is this non-conformal deposition at operation 150 whichis to generate air gaps within the space remaining between thetopographic features to reduce the interconnect capacitance relative tothe ILD structure illustrated in FIG. 2A. As shown in FIG. 2F, due tothe non-conformality of the low-k ILD 250, an air gap 255 is formedbetween adjacent metal interconnect lines 205A, 205B in the region ofthe trench 230 not occupied by the dielectric diffusion barrier 240.Hence, it should be clear that reducing the thickness of the dielectricdiffusion barrier 240 by 1 unit (e.g., 8 nm) can increase the width ofthe air gap 255 by 2 units (e.g., 16 nm) and therefore result in a netimprovement (i.e., reduction) in capacitance even though a high-kmaterial may be introduced to some extent within the dielectricdiffusion barrier 240.

Referring still to FIG. 2F, in embodiments the, low-k ILD 250 is SiOC:Hwith a dielectric constant in the range of 2.5- 3.1. In certain otherembodiments, the low-k ILD 250 is a porous film having a dielectricconstant below about 2.5. As known, in the art, a chemical-mechanicalplanarization (CMP) process may be employed to planarized the surface ofthe low-k ILD 250.

Returning to FIG. 1, the method 100 continues at operation 160 where thedevice is completed with conventional processing and fabricationtechniques know in the art. For example, as illustrated in FIG. 2G, anadditional level of metal interconnect 260 is disposed in the low-k ILD250. As shown, the metal interconnect 260 is coupled to the metalinterconnect 205 by a metal-filled (Cu) via passing through thedielectric diffusion barrier 240 and any remaining hardmask layer 220.Additional air-gaps may then be formed in the second-level of metalinterconnect substantially as described elsewhere herein in the contextof operations 110-150.

FIGS. 3A-3B illustrate line graphs for experimental evaluations ofdielectric diffusion barrier embodiments, in accordance with embodimentsof the present invention. Stress measurements were collected for a filmstack including the dielectric diffusion barrier treatment over a thickmoisture absorbing oxide which registers a change in stress measured viawafer bow and correlated with moisture content. The FIG. 3A shows a flatline trend for an ALD layer of Al₂O₃ of 6 nm and greater serve as amoisture diffusion barrier (hermetic barrier). For thicknesses below 6nm, wafer bow changes over time indicating the moisture is penetratingthe Al₂O₃ layer. FIG. 3B is a line graph for a SiON(C):H/AlO_(x) bilayerdielectric diffusion barrier. As can be seen, a 6 nm SiON(C):H layer 2nm AlO_(x) layer shows little moisture absorption. This is representsmore than a 60% reduction in thickness of the high-k Al₂O₃ needed toform a conformal barrier and therefore capacitance may be advantageouslyreduced while still providing an extremely thin hermetic barrier (e.g.,8 nm). For reference, at least 14 nm of SiON(C) is needed to providesimilar results. In reference to embodiments of a silicon alloyed metaloxide diffusion barrier (e.g., metal silicate), though not explicitlydepicted in a plot it is noted that because SiON layer with an oxygencontent twice the nitrogen content has been found to maintain ahermeticity equivalent of SiN compositions, it is expected that metalsilicate (e.g., aluminosilicates, Al_(1−y)Si_(y)O_(x), magnesiosilicates(Mg_(1−y)Si_(y)O_(x)), etc.) films where up to 50% of the metal speciesis replaced by Si will also maintain the hermeticity of thecorresponding metal oxide.

FIG. 4 illustrates a computing device 1000 in accordance with oneimplementation of the invention. The computing device 1000 houses aboard 1002. The board 1002 may include a number of components, includingbut not limited to a processor 1004 and at least one communication chip1006. The processor 1004 is physically and electrically coupled to theboard 1002. In some implementations, at least one communication chip1006 is also physically and electrically coupled to the board 1002. Infurther implementations, the communication chip 1006 is part of theprocessor 1004.

Depending on its applications, computing device 1000 may include othercomponents that may or may not be physically and electrically coupled tothe board 1002. These other components include, but are not limited to,volatile memory (e.g., DRAM), non-volatile memory (e.g., ROM), flashmemory, a graphics processor, a digital signal processor, a cryptoprocessor, a chipset, an antenna, a display, a touchscreen display, atouchscreen controller, a battery, an audio codec, a video codec, apower amplifier, a global positioning system (GPS) device, a compass, anaccelerometer, a gyroscope, a speaker, a camera, and a mass storagedevice (such as hard disk drive, compact disk (CD), digital versatiledisk (DVD), and so forth).

The communication chip 1006 enables wireless communications for thetransfer of data to and from the computing device 1000. The term“wireless” and its derivatives may be used to describe circuits,devices, systems, methods, techniques, communications channels, etc.,that may communicate data through the use of modulated electromagneticradiation through a non-solid medium. The term does not imply that theassociated devices do not contain any wires, although in someembodiments they might not. The communication chip 1006 may implementany of a number of wireless standards or protocols, including but notlimited to Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16 family), IEEE802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE,GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, derivatives thereof, as well asany other wireless protocols that are designated as 3G, 4G, 5G, andbeyond. The computing device 1000 may include a plurality ofcommunication chips 1006. For instance, a first communication chip 1006may be dedicated to shorter range wireless communications such as Wi-Fiand Bluetooth and a second communication chip 1006 may be dedicated tolonger range wireless communications such as GPS, EDGE, GPRS, CDMA,WiMAX, LTE, Ev-DO, and others.

The processor 1004 of the computing device 1000 includes an integratedcircuit die packaged within the processor 1004. In some implementationsof the invention, the integrated circuit die of the processor includesone or more devices, such as metal interconnects with a dielectricdiffusion barrier disposed there between as described elsewhere herein.The term “processor” may refer to any device or portion of a device thatprocesses electronic data from registers and/or memory to transform thatelectronic data into other electronic data that may be stored inregisters and/or memory.

The communication chip 1006 also includes an integrated circuit diepackaged within the communication chip 1006. In accordance with anotherimplementation of the invention, the integrated circuit die of thecommunication chip includes one or more devices such as metalinterconnects with a dielectric diffusion barrier disposed there betweenas described elsewhere herein.

In further implementations, another component housed within thecomputing device 1000 may contain an integrated circuit die thatincludes one or more devices, such as metal interconnects with adielectric diffusion barrier disposed there between as describedelsewhere herein.

In various implementations, the computing device 1000 may be a laptop, anetbook, a notebook, an ultrabook, a smartphone, a tablet, a personaldigital assistant (PDA), an ultra mobile PC, a mobile phone, a desktopcomputer, a server, a printer, a scanner, a monitor, a set-top box, anentertainment control unit, a digital camera, a portable music player,or a digital video recorder. In further implementations, the computingdevice 1000 may be any other electronic device that processes data.

The above description is illustrative, and not restrictive. For example,while flow diagrams in the figures show a particular order of operationsperformed by certain embodiments of the invention, it should beunderstood that such order may not be required (e.g., alternativeembodiments may perform the operations in a different order, combinecertain operations, overlap certain operations, etc.). Furthermore, manyother embodiments will be apparent to those of skill in the art uponreading and understanding the above description. Although the presentinvention has been described with reference to specific exemplaryembodiments, it will be recognized that the invention is not limited tothe embodiments described, but can be practiced with modification andalteration within the spirit and scope of the appended claims. The scopeof the invention should, therefore, be determined with reference to theappended claims, along with the full scope of equivalents to which suchclaims are entitled.

What is claimed is:
 1. A method of fabricating a microelectronic device, the method comprising: forming a pair of adjacent metal interconnect lines over a substrate, the pair of interconnect lines separated by a space; forming an air gap within a low-k interlayer dielectric (ILD) material disposed in the space between the metal interconnect lines; and forming a contiguous dielectric diffusion barrier that is a multilayer film stack spanning the space, the multilayer film stack comprising a first material layer on a second material layer between the air gap and a portion of the low-k ILD material on a sidewall of at least one of the metal interconnect lines, wherein at least one of the first material layer and the second material layer comprises a metal species and oxygen, and wherein forming the diffusion barrier comprises depositing the at least one of the first material layer and the second material layer using an atomic layer deposition (ALD) process.
 2. The method claim 1, wherein depositing the at least one of the first material layer and the second material comprises depositing a layer of high-k dielectric material having a dielectric constant between 8 and
 10. 3. The method of claim 2, wherein the layer of high-k dielectric material consists essentially of one of: Al₂O₃, MgO₂, and HfO₂.
 4. The method of claim 1, further comprising passivating an exposed surface of the pair of metal interconnect lines by performing a PECVD deposition of a SiCN:H, SiC:H, or SiOC:H film prior to performing the ALD process.
 5. The method of claim 2, wherein forming the dielectric diffusion barrier further comprises alloying the high-k dielectric material with silicon to form a metal silicate having a dielectric constant below
 7. 6. The method of claim 5, wherein alloying the high-k dielectric material with silicon further comprises cyclically depositing, with an ALD process, Al₂O₃ layers and SiO₂ layers to form aluminosilicate (Al_(y)Si_(1-y)O_(x)) or MgO₂ layer and SiO₂ layers to form magnesiosilicate (Mg_(y)Si_(1-y)O_(x)).
 7. The method of claim 1, wherein forming the dielectric diffusion barrier further comprises depositing by PECVD a layer of intermediate-k dielectric material having a dielectric constant below that of the high-k dielectric material and above that of the low-k dielectric material.
 8. The method of claim 7, wherein the dielectric diffusion barrier is deposited to a thickness less than 10 nm and wherein the intermediate-k dielectric material comprises carbon-doped silicon oxynitride.
 9. The method of claim 1, wherein forming the contiguous dielectric diffusion barrier spanning the space, further comprises: etching a trench in a first layer of the low-k ILD disposed between the pair of metal interconnect lines; and lining the trench with the dielectric diffusion barrier, and wherein forming the air gap further comprises depositing a second ILD layer with a non-conformal process.
 10. The method of claim 1, further comprising etching an opening through a region of the dielectric diffusion barrier disposed over one of the interconnect metal lines, and forming a second level metal interconnect via through the opening. 